The present invention relates to rotary regenerative air preheaters having sector plates dividing the air preheater into a gas sector and one or more air sectors and having radial seals and static seals which cooperate with the sector plates to reduce the leakage between the air preheater sectors. More particularly, the invention relates to a novel arrangement of the static seals and sector plates for improved performance.
A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor, which is packed with the heat transfer surface, is divided into compartments by a number of radially extending plates referred to as diaphragms. These compartments are adapted to hold modular baskets in which the heat transfer surface is contained.
The air preheater is divided into a flue gas side or sector and one or more combustion air sides or sectors by pie-shaped, radially disposed sector plates. Flexible radial seals on the rotor, usually mounted on the top and bottom edges of the diaphragms, engage or are in close proximity to these sector plates and minimize leakage of gas and air between sectors through the space between the rotor and the sector plates. Likewise, static seals mounted to the air preheater casing cooperate with the sector plates to minimize the leakage through the space between the sector plates and the casing.
The existing arrangements of static seals and sector plates incorporate static seals on one or both of the side edges of the sector plates. The sector plates can move with respect to the static seals during operation but still maintain sealing engagement. In addition, the sector plates are pinned against arcuate and radial displacement. Pinning arrangements are employed near the central hub of the air preheater and at a center point near the outer ends of the sector plates to keep the sector plates on center and to resist the lateral pressure loading on the sector plates caused by the differential in pressure between the higher pressure air and the lower pressure gas.
Because the orientation of static seals is presently along the air and/or gas edges of the sector plates, additional loading may be imposed to both the pinning arrangement and static seals due to thermal growth differentials. In addition, the sector plates on the top of the air preheater often accumulate excessive ash which may be trapped between the sector plates and the external casing of the air preheater causing interference with relative movement. This can be a significant problem which can actually result in the deformation of the sector plate and can result in higher axial loads being transmitted to supports. Other problems can occur with present designs where static seals are employed along both radial sides of the sector plates. One problem is the interference between the sector plate and the two opposing static seals due to differential thermal growth as between the static seals and the pinning arrangement. Another problem is the potential thermal distortion of the sealing face of the sector plate due to a differential temperature between the sealing face of the sector plate and the opposite shielded face of the sector plate adjacent the casing.